1. Field of the Invention
The present invention relates generally to a method of manufacturing an optical waveguide and more particularly to a method of manufacturing an optical waveguide, in which the number of manufacturing steps is reduced with respect to known manufacturing techniques.
2. Description of the Related Art
In the modern information-orientated society, a great deal of information needs to be exchanged at high speed and optical communication is indispensable for such high-speed exchange of information. The phrase "fiber to the home (FTTH)," is becoming increasingly used to refer to optical communication networks having runs to individual homes.
However, optical waveguides must be formed to very precise tolerances and should meet the following requirements: stability of shape of a core portion, roughness of interface between a core and a cladding, and smallness in amount of near infrared (1.3 to 1.5 .mu.m) light absorbed in glass material of the core and cladding.
A conventional process of manufacturing an optical waveguide comprises many steps such as film forming steps with use of a vacuum apparatus. Examples of conventional steps for manufacturing an optical waveguide will now be described with reference to FIG. 1.
At first, a silicon dioxide (SiO.sub.2) substrate 90 which will become a cladding layer of the optical waveguide is prepared (STEP 1).
The upper surface of the SiO.sub.2 substrate 90 prepared in step 1 is coated by CVD (chemical vapor deposition) with a film of a substance having a higher refractive index than SiO.sub.2, e.g. Ge-SiO.sub.2 film, to a thickness of about several .mu.m (STEP 2). The Ge-SiO.sub.2 film 91 will become a core of the optical waveguide.
A photoresist 92 with a thickness of about several .mu.m is coated on the Ge-SiO.sub.2 film 91 deposited in STEP 2 (STEP 3).
The photoresist 92 coated in STEP 3 is exposed with ultraviolet radiation and developed so that the optical waveguide has a desired circuit configuration (STEP 4). Thus, only that portion of the photoresist 92, which corresponds to the desired circuit configuration, is left.
With the photoresist 92 exposed and developed in STEP 4 being used, the Ge-SiO.sub.2 film 91 is etched away (STEP 5). Thus, only that portion of the Ge-SiO.sub.2 film 91, which corresponds to the circuit configuration, is left.
The photoresist 92 left in STEP 4 is removed (STEP 6).
An SiO.sub.2 film 93 with a thickness of about several .mu.m, which will become a cladding layer of the optical waveguide, is coated by CVD on the SiO.sub.2 substrate 90 and Ge-SiO.sub.2 film 91 (STEP 7).
Thus, the optical waveguide, which comprises the SiO.sub.2 substrate 90 serving as cladding, the Ge-SiO.sub.2 film 91 serving as core and the SiO.sub.2 film 93 serving as cladding, is formed.
In STEPS 2 and 7, the coating layers are formed by a so-called deposition process such as chemical vapor deposition (CVD), flame hydrolysis deposition (FHD) or physical vapor deposition (PVD), or by a sol-gel method. The etching in STEP 5 is performed by reactive ion etching (RIE), etc. These manufacturing steps are performed by using a vacuum apparatus, and a great deal of time and cost is required.
The above-described conventional method of manufacturing the optical waveguide requires many manufacturing steps and a great deal of time, resulting in a high manufacturing cost. This poses a serious problem in development of optical communication networks.